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Overdrive causing gearbox issue


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Hello All,

New to the forum, so any help/guidance would be much appreciated.

I have a 1974 Series 3 SWB. After saving up for a long time I recently bought a refurbished Fairey overdrive from a local chap. We fitted the overdrive (well he did I watched) & it ran sweetly (no whine etc....). However I noticed that on overrun in 2nd gear (foot off throttle just slowing/crawling along) she would jump, violently, out of 2nd gear.

I know old Land Rovers can jump out of gear & for a day or two I convinced myself it was just one of those things.

This morning we made the hole for the overdrive lever a bit bigger as it was a little tight & when we went to move the Land Rover it wouldn't engage gear. We figured that moving the lever back & forth as making the hole bigger had moved or broken something in the overdrive (the chap who installed thought perhaps some little ball bearings that can sometimes come loose), so we simply took the overdrive off & the chap who installed it is going to take it apart.

The strange thing, & the reason for this post, is that now the Land Rover is back to 'standard' with no overdrive she doesn't jump out of 2nd gear !!!

Could it be that something in the overdrive wasn't tight or knackered ? as I mentioned earlier in post, when the overdrive was engaged it ran very sweetly.

Any light you guys can shed on this would be great.

Thanks, Tim

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Jumping out of second gear is a symptom of a loose rear nut on the gear box main shaft. Since you've just had this nut undone to replace the transfer box input gear with the overdrive clutch sleeve, this is even more likely.

Did you fit the tab washer to lock the nut after applying about 100'lbs of torque? The tabs on a standard washer need filing down about 1mm to fit the overdrive, and the specially made overdrive version are hard to find. Running without the tab washer or forgetting to fold a tab down would allow the nut to slacken of very quickly.

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Many thanks Snagger. I will check with the chap who's done it for me. I have a nagging feeling he said that the castelated nut on the back of the main shaft had to come off when fitting the overdrive as the overdrive wouldn't go on with the nut in place - I'll ask him to confirm this. If he has it stands to reason, as you say. Whilst it's a pain & I'm a natural worrier about the damage this may have done, I'm pleased that the gearbox seems ok.

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If I understand your post correctly and he left he nut off, then don't ever let him near the car again - he may owe you a new gear box if there is any damage. The nut, the tab washer (with a tiny trim) and the spacer washer all have to be refitted after swapping the gear for the clutch sleeve. Running with a loose nut can cause damage, and running without a nut will destroy the gear box in very short order. Anyone making that mistake should not be fiddling with anything technical.

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